(1) Field of the Invention
This disclosure pertains to an electronic control circuit for high intensity fiber optic light sources used in surgery, dentistry, and other applications such as inspection of aircraft and the like where a fiber optic cable carries light to the point of use to provide a high intensity light.
(2) Description of the Prior Art
Modern enclosed arc lamps as made by G.E. and others have natural characteristics that require a certain sequence of operations to place them into condition to ignite and then to continue illumination after ignition. Also, the lamp intensity can be varied from its maximum intensity to a usable low intensity once the lamp has gained a certain operating condition.
Power supplies are now manufactured that provide the sequence of operations necessary for proper illumination. Also, these power supplies now furnish the necessary electronic circuitry to vary the intensity of the lamp after initial ignition. However, the point at which an operator may adjust the lamp intensity, without extinguishing the lamp, is determined by the operator, and is not automatic. Further, if the intensity setting is low at the time the unit is turned on, the arc lamp will not receive the required voltage to trigger itself into an on condition. This invention provides a circuit which allows the lamp to trigger regardless of the setting of the brightness control. This disclosure shows a circuit which utilizes the lamp's own electronic condition to automatically energize the dimming circuit to cut in and engage when all conditions are correct for proper illumination and for proper dimming control.
Prior high intensity lamps (enclosed arc lamps) are triggered initially through a capacitor which is discharged causing a high voltage surge (approx. 7500 volts) across the lamp electrodes. This initial voltage surge causes minute ionization reducing the gas resistance sufficiently to permit a second, highly capacitive discharge (approx. 160 volts DC), to flow across the lamp electrodes, further ionizing the gases and initiating illumination.
After these initial voltage surges, the power supply controls the amperage permitted to flow in the lamp at approximately 7.8 amperes d.c. However, at the 7.8 amp. level, the voltage across the electrodes will initially drop to approximately 12 volts d.c. Next, the power supply will permit the voltage across the lamp electrodes to rise to its normal full illumination of 35 to 45 volts d.c., while the amperage is maintained at 7.8 amperes. Until the lamp has received and conditioned itself to approximately 24 volts d.c., the dimming control which reduces the amperage across the lamp electrodes, and, adjusts the intensity of the lamp, should not be used. If the dimming control was permanently wired into the lamp ignition circuit, and the control potentiometer set to a low position, the power circuit could not control the lamp and place it into an ignition condition. Under such a low illumination setting, it would then be necessary to increase the control potentiometer setting (increase the brightness setting) before a successful ignition could occur.
The above facts regarding inability of the lamp to trigger if the brightness control is at a low setting may seem insignificant at first reading until a few other factors are considered. Personnel using this equipment would only know of this lamp characteristic and inability to trigger at a low intensity setting by studying the operating manual, or, using the instrument on many occasions to familiarize themselves with it. Unfortunately, a manufacturer of instruments sold to the general public must realize ideal conditions never exist and regardless of previous explanation, customers demand the unit works when they flip the switch.
Another point and a more irritating one to our customers is the fact that the enclosed arc lamp has a delay in trying to restart itself once it has been ignited, even if ignited only for a very short period of time. This is a natural characteristic of the gases used in the lamp construction. The lamp can start easily in a cold condition; however, once the gases are warmed up, the lamp will not restart until the gases have cooled again to a certain level. In a fully illuminated lamp, delay can be a time interval of a full minute while in false starts it is, of course, a lesser time, but nevertheless irritating. Because of these facts, it is necessary that an automatic means be provided for the lamp to properly ignite, remain ignited until ready for dimming control, and then the actual dimming control be electronically connected when ready.
Problems involved in the prior art are overcome by the instant invention which provides an automatic triggering of the light source regardless of the intensity setting of a control knob on the control panel and its associated control potentiometer.